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Author
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Topic: High Rpm miss. Fuel pump?
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Built351c
Gearhead Posts: 140
From: Big Lake, MN
Registered: Dec 2001
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posted 08-04-2002 10:34 PM
 
When I floor the car it gets up to 5000 rpm and starts missing. Sometimes around 5500rpm. I checked the fuel pressure and have it set at 8 1/2lbs. Its a Holley Blue electric fuel pump going into 1/2 inch fuel line up to the reg and then into 3/8 line to the carb. The ignition is a MSD 6A and blaster2 coil and msd electronic dist. When I slowly bring up the rpm the car starts missing at 4000 rpm. Yet it idles and runs fine otherwise on the street and highway. No black smoke and the plugs look perfect. The ignition setup is brand new and did not have any problems the year before.
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Rustang
Gearhead Posts: 880
From: Clarion PA
Registered: Nov 2000
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posted 08-04-2002 10:44 PM
This is probably a dumb question but is the miss under load or free reving?------------------
'68 mustang 351 clevor- 10.92@124
'67 Stang, 351W -11.18@118
'69 351C Torino-14.90@100
'78 Pickup 351W-15.56@88
'79 Pickup 460 ET=??
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Built351c
Gearhead Posts: 140
From: Big Lake, MN
Registered: Dec 2001
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posted 08-04-2002 10:52 PM
Under load
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kid vishus
Gearhead Posts: 7251
From: middle of NC
Registered: Oct 2000
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posted 08-04-2002 11:15 PM
Is it a solid cam or a hydroulic? A lot of the times, when the springs start to go bad it will act just like a fuel delivery problem. ------------------
Rob Hetzler
member #773
'69 mustang, 351C, 9.97 @ 133 mph 1/4, 6.27 @ 108 1/8, 1.344 60'
'70 mustang, flintstone power
'93 F150 Lightning 15.33 @ 87 mph, completely stock with 149k miles
'99 Pro Et track champion
'00 Mod ET R-up (with new car) My Photo Page
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Built351c
Gearhead Posts: 140
From: Big Lake, MN
Registered: Dec 2001
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posted 08-04-2002 11:16 PM
Solid Roller - Not even 5000 miles on the motor yet.
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Rory McNeil
Gearhead Posts: 1889
From: Surrey, B.C. Canada
Registered: Nov 2000
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posted 08-05-2002 01:26 AM
Doubt it`s the fuel pump, if it can`t keep up, you can usually wind it out in 1rst,& 2nd (on a stick), or most of the way thru 2nd with an auto. before it`ll lay down. Considering that it does it even in 1rst, at only 5000 rpm, I`d be checking ignition or valve springs. You say you have a solid roller, what are your valve spring pressures, & were they all tested & installed at the correct height? Years ago a friend had a moderate sized roller in his 440 Mopar, after struggling with a bad high rpm miss for over a year, he brought it to another friends shop. It turns out the original engine builder "felt" that 145lbs on the seat should be adequate. He was WRONG! Shimmed the springs up to 180 on the seat, & cured the miss & knocked off 1/2 second of ET.------------------
78 Fairmont 428 4 speed 10.20@130mph
80 Fairmont 302 5 speed 12.8@105mph
85 Mustang NHRA Stocker under construction, 302 5 speed
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kid vishus
Gearhead Posts: 7251
From: middle of NC
Registered: Oct 2000
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posted 08-05-2002 10:06 AM
The first motor I ever built, had a solid flat tappet cam in it. Unfortunatley for me, the shop that did the work felt that 90#'s of seat pressure was enough.  The motor had a built in rev limiter. Once the springs got changed, the motor would wind to the moon. I would look at valve springs, or ignition, like Rory said. When I was running a Holley blue pump on the granada, it got down into the 11.30 range with one pump before it became inadequete. And that was shifting at 7000 rpm. Then it started to lay down right at the end of 2nd gear, and right before the lights in the qrtr.
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70coupe
Gearhead Posts: 493
From: Toronto,Ontario,Canada
Registered: Aug 2000
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posted 08-05-2002 10:37 AM
I would guess ignition. If its the fuel pump the car would probably nose dive a bit or you would hear a popping noise if it went lean. Try something simple like a new cap and rotor and check your timing.
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jsracingbbf
unregistered
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posted 08-05-2002 10:02 PM
Check your springs, even if that isn't it you need to know where they are. I always do my own heads. As far as setting up the springs. All you need is a press, spring height mic, and a spring tester that is used in a press, NOT one of those you check on the car. It is good for quick checks, or as a baseline, after you install new springs, but don't set your heads up with it. I put my heads on a good clean bench and use a c-clamp and spring compressor to set them up. I write down all installed heights. Make sure to check the Spring manufacturer's compressed spring heigth, you don't want coil bind. Comp cams can sell you shims, cups, offset retainers, offset keepers or whatever. You can get the machine shop to cut the seats but double check them with some ( fine ) lapping compound yourself. I then let them sit overnight with gas in each port and then the combustion chamber, this helps find any leaks. It isn't fool proof but it's better than what you get at most machine shops. This is cheap insurance rather than find a problem later. ------------------
Jerry Smith
69 Mustang Pro ET Drag
"Even a blind hog can find an acorn every now and then "
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Built351c
Gearhead Posts: 140
From: Big Lake, MN
Registered: Dec 2001
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posted 08-11-2002 01:27 AM
Found the problem. It was the carb. I switched carbs with my brother. He had a speed demon 850. My old carb was a Predator carb. All I can say is. .. My car Flew with the demon. It was out of control. The car felt like it was on ice. Even at 60mph the car could light them up and swing the back end around if I let it. Getting rid of the predator carb. Looking at getting new carb now. It was unf***ing beleiveable. I cannot describe what a difference. When I got back home I had a smile on my face that went all the way around my head. Next on the to buy list:New carb - recommendations? Deep grove pullys - keeps throwing the belts off at upper rpms. New rims and tires - G-60 14inch dont work. In case any one wants to know whats in the car. 1970 351c .20 overbore
2- bolt mains studded with ARP Main stud kit
Blueprinted, balanced
Linehone mains
Index block and Torque Hone block with deck plates
Shotpeen and Resize rods and install ARP bolts
Hone Rods for full floating pins
Drill rods for pin oiling
Static and Spin Balance
Prep Crank
Polish & Chamfer crank
Grind Crank .020-.020
File fit Z-Gap Rings
Lunati Custom Light Weight Pistions
Lunati Solid Roller Cam
The spec's:
Lift at valve
.650 In. and .650 Ex.
Duration at .050 Tappet lift
260 In. and 268 Ex.
Advertised Duration
293 In. and 307 Ex.
Valve Adjustment
.026 In. and .026 Ex.
108 Lobe separation 351 4v 1970 closed chamber with a mild clean up flowed these numbers.
INTAKE
.100-70cfm
.200-132.8 cfm
.300-192.6 cfm
.400-242.8 cfm
.500-278.4 cfm
.600-293.0 cfm
.700-301.0 cfm
.800-301.0 cfm EXHAUST
.100-56.6 cfm
.200-103.6 cfm
.300-143.5 cfm
.400-173.9 cfm
.500-195.3 cfm
.600-203.5 cfm
.700-206.6 cfm
.800-208.5 cfm
1970 Closed chamber heads
Hardened Alloy Valve Guides
Hardened Exhaust Seats
Stainless 2.190 Intakes Valves
Stainless 1.750 Exhaust Valves
11/32 Full Bronze valve guides
.030 Hardened Lunati shims
11/32x.500 Postive teflon valve seals
Vasco Jet Roller springs
Lunati Titanium Retainers
Lunati Spring cups
Lunati Machined 10 degree Locks
ARP Screw in rocker studs
Manley Guide Plates 3/8
Lunati Roller rockers 1.73
Lunati stud poly locks
Lunati pro-series push rods
Carb - Predator carburator 1 inch spacer
Intake - Wieand X-celerator
Headers - Hooker supercomp 1 7/8
C-4 - 4000 stall
3.89 Traction-Loc.
3inch with X-pipe Dyno-max Ultra-Flow duel exhaust. - Sounds Sweet. Car: 1969 Mach 1 - 3240lbs w/o driver.
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kid vishus
Gearhead Posts: 7251
From: middle of NC
Registered: Oct 2000
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posted 08-11-2002 10:52 AM
I would put a 750 HP Holley on it. The problem with the Demon carbs is, they are made by BG, and some of them work, and some of them dont. Your brother got a good one, but you might not. And BG's tech support sux, as does their service of their carbs. The Holleys all seem to work really well.
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Built351c
Gearhead Posts: 140
From: Big Lake, MN
Registered: Dec 2001
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posted 08-12-2002 09:11 PM
Would a 750 HP be big enough? My brothers carb was a 850 and the car loved it. I never felt that much power from my car before. It completely left me with a grin for the next two weeks. Also the car likes to throw the belts when I rev it past 6000rpm. Looking at some undrive pullys. summit racing has a set for $305.00. That includes the Crank,power steering, alt and water pump. What do you use on your car kid?
Man is my jaw going to be sore when I stop smiling. 
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